HONOLULU — The first storm in a one-two punch that sent Hawaii scrambling to brace itself weakened on its approach to the state, while a second system close behind was largely expected to pass north of the islands.

The National Weather Service downgraded Iselle to a tropical storm about 50 miles before it was expected to make landfall early today in the southern part of Hawaii’s Big Island. Wind and rain from the system still had enough oomph to knock down trees, cause power outages and block some roads. No deaths or major injuries were reported late Thursday.

Iselle was classified as a tropical storm at 11 p.m. Thursday Hawaii Standard Time when its winds slowed to 70 mph, putting it below the minimum of 74 mph for a hurricane.

The storm was weakening because of several factors, including wind shear chopping at the system and the Big Island’s terrain above the water, said Chris Brenchley, meteorologist with the National Weather Service in Honolulu.

“It can start to feel the drain,” he said. “As wind blows into the terrain, the terrain kind of redirects the wind.”